Java upgrade guides and Java Collection (#260)
* Java 25 upgrade guide with best practices (Java 21 -> 25) Added a description for the Java upgrade guide. * Add Java Development Collection and Upgrade Guides - Created a new collection for Java development, including prompts and instructions for Spring Boot, Quarkus, JPA, JUnit, and Javadoc. - Added comprehensive markdown documentation for upgrading from Java 17 to Java 21, detailing new language features, API changes, and best practices. - Introduced upgrade guide for transitioning from Java 21 to Java 25, highlighting new features, migration strategies, and performance considerations. * Update upgrade guide headers and descriptions for Java 21 to 25 * Refactor Java Development Collection: Update Upgrade Guides with Descriptions * Add Java 11 to Java 17 Upgrade Guide with best practices and migration patterns * Rename files
This commit is contained in:
Bruno Borges
GitHub
parent
b7e46f9d50
commit
6906627e07
@ -20,6 +20,7 @@ Curated collections of related prompts, instructions, and chat modes organized a
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| [Database & Data Management](collections/database-data-management.md) | Database administration, SQL optimization, and data management tools for PostgreSQL, SQL Server, and general database development best practices. | 8 items | database, sql, postgresql, sql-server, dba, optimization, queries, data-management |
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| [DevOps On-Call](collections/devops-oncall.md) | A focused set of prompts, instructions, and a chat mode to help triage incidents and respond quickly with DevOps tools and Azure resources. | 5 items | devops, incident-response, oncall, azure |
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| [Frontend Web Development](collections/frontend-web-dev.md) | Essential prompts, instructions, and chat modes for modern frontend web development including React, Angular, Vue, TypeScript, and CSS frameworks. | 11 items | frontend, web, react, typescript, javascript, css, html, angular, vue |
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| [Java Development](collections/java-development.md) | Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices. | 12 items | java, springboot, quarkus, jpa, junit, javadoc |
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| [Project Planning & Management](collections/project-planning.md) | Tools and guidance for software project planning, feature breakdown, epic management, implementation planning, and task organization for development teams. | 17 items | planning, project-management, epic, feature, implementation, task, architecture, technical-spike |
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| [Security & Code Quality](collections/security-best-practices.md) | Security frameworks, accessibility guidelines, performance optimization, and code quality best practices for building secure, maintainable, and high-performance applications. | 6 items | security, accessibility, performance, code-quality, owasp, a11y, optimization, best-practices |
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| [Technical Spike](collections/technical-spike.md) | Tools for creation, management and research of technical spikes to reduce unknowns and assumptions before proceeding to specification and implementation of solutions. | 2 items | technical-spike, assumption-testing, validation, research |
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@ -49,6 +49,9 @@ Team and project-specific instructions to enhance GitHub Copilot's behavior for
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| [Gilfoyle Code Review Instructions](instructions/gilfoyle-code-review.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgilfoyle-code-review.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgilfoyle-code-review.instructions.md) | Gilfoyle-style code review instructions that channel the sardonic technical supremacy of Silicon Valley's most arrogant systems architect. |
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| [GitHub Actions CI/CD Best Practices](instructions/github-actions-ci-cd-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgithub-actions-ci-cd-best-practices.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgithub-actions-ci-cd-best-practices.instructions.md) | Comprehensive guide for building robust, secure, and efficient CI/CD pipelines using GitHub Actions. Covers workflow structure, jobs, steps, environment variables, secret management, caching, matrix strategies, testing, and deployment strategies. |
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| [Go Development Instructions](instructions/go.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgo.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fgo.instructions.md) | Instructions for writing Go code following idiomatic Go practices and community standards |
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| [Java 11 to Java 17 Upgrade Guide](instructions/java-11-to-java-17-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-11-to-java-17-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-11-to-java-17-upgrade.instructions.md) | Comprehensive best practices for adopting new Java 17 features since the release of Java 11. |
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| [Java 17 to Java 21 Upgrade Guide](instructions/java-17-to-java-21-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.instructions.md) | Comprehensive best practices for adopting new Java 21 features since the release of Java 17. |
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| [Java 21 to Java 25 Upgrade Guide](instructions/java-21-to-java-25-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.instructions.md) | Comprehensive best practices for adopting new Java 25 features since the release of Java 21. |
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| [Java Development](instructions/java.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md) | Guidelines for building Java base applications |
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| [Joyride User Scripts Project Assistant](instructions/joyride-user-project.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-user-project.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-user-project.instructions.md) | Expert assistance for Joyride User Script projects - REPL-driven ClojureScript and user space automation of VS Code |
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| [Joyride Workspace Automation Assistant](instructions/joyride-workspace-automation.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-workspace-automation.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjoyride-workspace-automation.instructions.md) | Expert assistance for Joyride Workspace automation - REPL-driven and user space ClojureScript automation within specific VS Code workspaces |
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collections/java-development.collection.yml
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collections/java-development.collection.yml
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id: java-development
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name: Java Development
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description: Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices.
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tags: [java, springboot, quarkus, jpa, junit, javadoc]
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items:
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- path: instructions/java.instructions.md
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kind: instruction
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- path: instructions/springboot.instructions.md
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kind: instruction
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- path: instructions/quarkus.instructions.md
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kind: instruction
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- path: instructions/quarkus-mcp-server-sse.instructions.md
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kind: instruction
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- path: instructions/convert-jpa-to-spring-data-cosmos.instructions.md
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kind: instruction
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- path: instructions/java-11-to-java-17-upgrade.instructions.md
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kind: instruction
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- path: instructions/java-17-to-java-21-upgrade.instructions.md
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kind: instruction
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- path: instructions/java-21-to-java-25-upgrade.instructions.md
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kind: instruction
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- path: prompts/java-docs.prompt.md
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kind: prompt
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- path: prompts/java-junit.prompt.md
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kind: prompt
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- path: prompts/java-springboot.prompt.md
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kind: prompt
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- path: prompts/create-spring-boot-java-project.prompt.md
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kind: prompt
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display:
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ordering: alpha
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show_badge: false
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22
collections/java-development.md
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collections/java-development.md
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# Java Development
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Comprehensive collection of prompts and instructions for Java development including Spring Boot, Quarkus, testing, documentation, and best practices.
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**Tags:** java, springboot, quarkus, jpa, junit, javadoc
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## Items in this Collection
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| Title | Type | Description |
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| ----- | ---- | ----------- |
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| [Convert Spring JPA project to Spring Data Cosmos](../instructions/convert-jpa-to-spring-data-cosmos.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fconvert-jpa-to-spring-data-cosmos.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fconvert-jpa-to-spring-data-cosmos.instructions.md) | Instruction | Step-by-step guide for converting Spring Boot JPA applications to use Azure Cosmos DB with Spring Data Cosmos |
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| [Create Spring Boot Java project prompt](../prompts/create-spring-boot-java-project.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fcreate-spring-boot-java-project.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fcreate-spring-boot-java-project.prompt.md) | Prompt | Create Spring Boot Java Project Skeleton |
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| [Java 11 to Java 17 Upgrade Guide](../instructions/java-11-to-java-17-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-11-to-java-17-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-11-to-java-17-upgrade.instructions.md) | Instruction | Comprehensive best practices for adopting new Java 17 features since the release of Java 11. |
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| [Java 17 to Java 21 Upgrade Guide](../instructions/java-17-to-java-21-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-17-to-java-21-upgrade.instructions.md) | Instruction | Comprehensive best practices for adopting new Java 21 features since the release of Java 17. |
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| [Java 21 to Java 25 Upgrade Guide](../instructions/java-21-to-java-25-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava-21-to-java-25-upgrade.instructions.md) | Instruction | Comprehensive best practices for adopting new Java 25 features since the release of Java 21. |
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| [Java Development](../instructions/java.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fjava.instructions.md) | Instruction | Guidelines for building Java base applications |
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| [Java Documentation (Javadoc) Best Practices](../prompts/java-docs.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-docs.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-docs.prompt.md) | Prompt | Ensure that Java types are documented with Javadoc comments and follow best practices for documentation. |
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| [JUnit 5+ Best Practices](../prompts/java-junit.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-junit.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-junit.prompt.md) | Prompt | Get best practices for JUnit 5 unit testing, including data-driven tests |
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| [Quarkus](../instructions/quarkus.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus.instructions.md) | Instruction | Quarkus development standards and instructions |
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| [Quarkus MCP Server](../instructions/quarkus-mcp-server-sse.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus-mcp-server-sse.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fquarkus-mcp-server-sse.instructions.md) | Instruction | Quarkus and MCP Server with HTTP SSE transport development standards and instructions |
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| [Spring Boot Best Practices](../prompts/java-springboot.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-springboot.prompt.md)<br />[](https://aka.ms/awesome-copilot/install/prompt?url=vscode-insiders%3Achat-prompt%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Fprompts%2Fjava-springboot.prompt.md) | Prompt | Get best practices for developing applications with Spring Boot. |
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| [Spring Boot Development](../instructions/springboot.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fspringboot.instructions.md)<br />[](https://aka.ms/awesome-copilot/install/instructions?url=vscode-insiders%3Achat-instructions%2Finstall%3Furl%3Dhttps%3A%2F%2Fraw.githubusercontent.com%2Fgithub%2Fawesome-copilot%2Fmain%2Finstructions%2Fspringboot.instructions.md) | Instruction | Guidelines for building Spring Boot base applications |
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793
instructions/java-11-to-java-17-upgrade.instructions.md
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793
instructions/java-11-to-java-17-upgrade.instructions.md
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---
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applyTo: ["*"]
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description: "Comprehensive best practices for adopting new Java 17 features since the release of Java 11."
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---
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# Java 11 to Java 17 Upgrade Guide
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## Project Context
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This guide provides comprehensive GitHub Copilot instructions for upgrading Java projects from JDK 11 to JDK 17, covering major language features, API changes, and migration patterns based on 47 JEPs integrated between these versions.
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## Language Features and API Changes
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### JEP 395: Records (Java 16)
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**Migration Pattern**: Convert data classes to records
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```java
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// Old: Traditional data class
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public class Person {
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private final String name;
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private final int age;
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public Person(String name, int age) {
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this.name = name;
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this.age = age;
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}
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public String name() { return name; }
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public int age() { return age; }
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@Override
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public boolean equals(Object obj) { /* boilerplate */ }
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@Override
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public int hashCode() { /* boilerplate */ }
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@Override
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public String toString() { /* boilerplate */ }
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}
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// New: Record (Java 16+)
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public record Person(String name, int age) {
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// Compact constructor for validation
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public Person {
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if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
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}
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// Custom methods can be added
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public boolean isAdult() {
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return age >= 18;
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}
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}
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```
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### JEP 409: Sealed Classes (Java 17)
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**Migration Pattern**: Use sealed classes for restricted inheritance
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```java
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// New: Sealed class hierarchy
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public sealed class Shape
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permits Circle, Rectangle, Triangle {
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public abstract double area();
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}
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public final class Circle extends Shape {
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private final double radius;
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public Circle(double radius) {
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this.radius = radius;
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}
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@Override
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public double area() {
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return Math.PI * radius * radius;
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}
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}
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public final class Rectangle extends Shape {
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private final double width, height;
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public Rectangle(double width, double height) {
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this.width = width;
|
||||
this.height = height;
|
||||
}
|
||||
|
||||
@Override
|
||||
public double area() {
|
||||
return width * height;
|
||||
}
|
||||
}
|
||||
|
||||
public non-sealed class Triangle extends Shape {
|
||||
// Non-sealed allows further inheritance
|
||||
private final double base, height;
|
||||
|
||||
public Triangle(double base, double height) {
|
||||
this.base = base;
|
||||
this.height = height;
|
||||
}
|
||||
|
||||
@Override
|
||||
public double area() {
|
||||
return 0.5 * base * height;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 394: Pattern Matching for instanceof (Java 16)
|
||||
|
||||
**Migration Pattern**: Simplify instanceof checks
|
||||
|
||||
```java
|
||||
// Old: Traditional instanceof with casting
|
||||
public String processObject(Object obj) {
|
||||
if (obj instanceof String) {
|
||||
String str = (String) obj;
|
||||
return str.toUpperCase();
|
||||
} else if (obj instanceof Integer) {
|
||||
Integer num = (Integer) obj;
|
||||
return "Number: " + num;
|
||||
} else if (obj instanceof List<?>) {
|
||||
List<?> list = (List<?>) obj;
|
||||
return "List with " + list.size() + " elements";
|
||||
}
|
||||
return "Unknown type";
|
||||
}
|
||||
|
||||
// New: Pattern matching for instanceof (Java 16+)
|
||||
public String processObject(Object obj) {
|
||||
if (obj instanceof String str) {
|
||||
return str.toUpperCase();
|
||||
} else if (obj instanceof Integer num) {
|
||||
return "Number: " + num;
|
||||
} else if (obj instanceof List<?> list) {
|
||||
return "List with " + list.size() + " elements";
|
||||
}
|
||||
return "Unknown type";
|
||||
}
|
||||
|
||||
// Works great with sealed classes
|
||||
public String describeShape(Shape shape) {
|
||||
if (shape instanceof Circle circle) {
|
||||
return "Circle with radius " + circle.radius();
|
||||
} else if (shape instanceof Rectangle rect) {
|
||||
return "Rectangle " + rect.width() + "x" + rect.height();
|
||||
} else if (shape instanceof Triangle triangle) {
|
||||
return "Triangle with base " + triangle.base();
|
||||
}
|
||||
return "Unknown shape";
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 361: Switch Expressions (Java 14)
|
||||
|
||||
**Migration Pattern**: Convert switch statements to expressions
|
||||
|
||||
```java
|
||||
// Old: Traditional switch statement
|
||||
public String getDayType(DayOfWeek day) {
|
||||
String result;
|
||||
switch (day) {
|
||||
case MONDAY:
|
||||
case TUESDAY:
|
||||
case WEDNESDAY:
|
||||
case THURSDAY:
|
||||
case FRIDAY:
|
||||
result = "Workday";
|
||||
break;
|
||||
case SATURDAY:
|
||||
case SUNDAY:
|
||||
result = "Weekend";
|
||||
break;
|
||||
default:
|
||||
throw new IllegalArgumentException("Unknown day: " + day);
|
||||
}
|
||||
return result;
|
||||
}
|
||||
|
||||
// New: Switch expression (Java 14+)
|
||||
public String getDayType(DayOfWeek day) {
|
||||
return switch (day) {
|
||||
case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY -> "Workday";
|
||||
case SATURDAY, SUNDAY -> "Weekend";
|
||||
};
|
||||
}
|
||||
|
||||
// With yield for complex logic
|
||||
public int calculateScore(Grade grade) {
|
||||
return switch (grade) {
|
||||
case A -> 100;
|
||||
case B -> 85;
|
||||
case C -> 70;
|
||||
case D -> {
|
||||
System.out.println("Consider improvement");
|
||||
yield 55;
|
||||
}
|
||||
case F -> {
|
||||
System.out.println("Needs retake");
|
||||
yield 0;
|
||||
}
|
||||
};
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 406: Pattern Matching for switch (Preview in Java 17)
|
||||
|
||||
**Migration Pattern**: Enhanced switch with patterns (Preview feature)
|
||||
|
||||
```java
|
||||
// Requires --enable-preview flag
|
||||
public String formatValue(Object obj) {
|
||||
return switch (obj) {
|
||||
case String s -> "String: " + s;
|
||||
case Integer i -> "Integer: " + i;
|
||||
case null -> "null value";
|
||||
case default -> "Unknown: " + obj.getClass().getSimpleName();
|
||||
};
|
||||
}
|
||||
|
||||
// With guarded patterns
|
||||
public String categorizeNumber(Object obj) {
|
||||
return switch (obj) {
|
||||
case Integer i when i < 0 -> "Negative integer";
|
||||
case Integer i when i == 0 -> "Zero";
|
||||
case Integer i when i > 0 -> "Positive integer";
|
||||
case Double d when d.isNaN() -> "Not a number";
|
||||
case Number n -> "Other number: " + n;
|
||||
case null -> "null";
|
||||
case default -> "Not a number";
|
||||
};
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 378: Text Blocks (Java 15)
|
||||
|
||||
**Migration Pattern**: Use text blocks for multi-line strings
|
||||
|
||||
```java
|
||||
// Old: Concatenated strings
|
||||
String html = "<html>\n" +
|
||||
" <body>\n" +
|
||||
" <h1>Hello World</h1>\n" +
|
||||
" <p>Welcome to Java 17!</p>\n" +
|
||||
" </body>\n" +
|
||||
"</html>";
|
||||
|
||||
String sql = "SELECT p.id, p.name, p.email, " +
|
||||
" a.street, a.city, a.state " +
|
||||
"FROM person p " +
|
||||
"JOIN address a ON p.address_id = a.id " +
|
||||
"WHERE p.active = true " +
|
||||
"ORDER BY p.name";
|
||||
|
||||
// New: Text blocks (Java 15+)
|
||||
String html = """
|
||||
<html>
|
||||
<body>
|
||||
<h1>Hello World</h1>
|
||||
<p>Welcome to Java 17!</p>
|
||||
</body>
|
||||
</html>
|
||||
""";
|
||||
|
||||
String sql = """
|
||||
SELECT p.id, p.name, p.email,
|
||||
a.street, a.city, a.state
|
||||
FROM person p
|
||||
JOIN address a ON p.address_id = a.id
|
||||
WHERE p.active = true
|
||||
ORDER BY p.name
|
||||
""";
|
||||
|
||||
// With string interpolation methods
|
||||
String json = """
|
||||
{
|
||||
"name": "%s",
|
||||
"age": %d,
|
||||
"city": "%s"
|
||||
}
|
||||
""".formatted(name, age, city);
|
||||
```
|
||||
|
||||
### JEP 358: Helpful NullPointerExceptions (Java 14)
|
||||
|
||||
**Migration Guidance**: Better NPE debugging (enabled by default in Java 17)
|
||||
|
||||
```java
|
||||
// Old NPE message: "Exception in thread 'main' java.lang.NullPointerException"
|
||||
// New NPE message shows exactly what was null:
|
||||
// "Cannot invoke 'String.length()' because the return value of 'Person.getName()' is null"
|
||||
|
||||
public class PersonProcessor {
|
||||
public void processPersons(List<Person> persons) {
|
||||
// This will show exactly which person.getName() returned null
|
||||
persons.stream()
|
||||
.mapToInt(person -> person.getName().length()) // Clear NPE if getName() returns null
|
||||
.sum();
|
||||
}
|
||||
|
||||
// Better error messages help with complex expressions
|
||||
public void complexExample(Map<String, List<Person>> groups) {
|
||||
// NPE will show exactly which part of the chain is null
|
||||
int totalNameLength = groups.get("admins")
|
||||
.get(0)
|
||||
.getName()
|
||||
.length();
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 371: Hidden Classes (Java 15)
|
||||
|
||||
**Migration Pattern**: Use for framework and proxy generation
|
||||
|
||||
```java
|
||||
// For frameworks creating dynamic proxies
|
||||
public class DynamicProxyExample {
|
||||
public static <T> T createProxy(Class<T> interfaceClass, InvocationHandler handler) {
|
||||
// Hidden classes provide better encapsulation for dynamically generated classes
|
||||
MethodHandles.Lookup lookup = MethodHandles.lookup();
|
||||
|
||||
// Framework code would use hidden classes for better isolation
|
||||
// This is typically handled by frameworks, not application code
|
||||
return interfaceClass.cast(
|
||||
Proxy.newProxyInstance(
|
||||
interfaceClass.getClassLoader(),
|
||||
new Class<?>[]{interfaceClass},
|
||||
handler
|
||||
)
|
||||
);
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 334: JVM Constants API (Java 12)
|
||||
|
||||
**Migration Pattern**: Use for compile-time constants
|
||||
|
||||
```java
|
||||
import java.lang.constant.*;
|
||||
|
||||
// For advanced metaprogramming and tooling
|
||||
public class ConstantExample {
|
||||
// Use dynamic constants for computed values
|
||||
public static final DynamicConstantDesc<String> COMPUTED_CONSTANT =
|
||||
DynamicConstantDesc.of(
|
||||
ConstantDescs.BSM_INVOKE,
|
||||
"computeValue",
|
||||
ConstantDescs.CD_String
|
||||
);
|
||||
|
||||
// Primarily used by compiler and framework developers
|
||||
public static String computeValue() {
|
||||
return "Computed at runtime, cached as constant";
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 415: Context-Specific Deserialization Filters (Java 17)
|
||||
|
||||
**Migration Pattern**: Enhanced security for object deserialization
|
||||
|
||||
```java
|
||||
import java.io.*;
|
||||
|
||||
public class SecureDeserialization {
|
||||
// Set up deserialization filters for security
|
||||
public static void setupSerializationFilters() {
|
||||
// Global filter
|
||||
ObjectInputFilter globalFilter = ObjectInputFilter.Config.createFilter(
|
||||
"java.base/*;java.util.*;!*"
|
||||
);
|
||||
ObjectInputFilter.Config.setSerialFilter(globalFilter);
|
||||
}
|
||||
|
||||
public <T> T deserializeSecurely(byte[] data, Class<T> expectedType) throws IOException, ClassNotFoundException {
|
||||
try (ByteArrayInputStream bis = new ByteArrayInputStream(data);
|
||||
ObjectInputStream ois = new ObjectInputStream(bis)) {
|
||||
|
||||
// Context-specific filter
|
||||
ObjectInputFilter contextFilter = ObjectInputFilter.Config.createFilter(
|
||||
expectedType.getName() + ";java.lang.*;!*"
|
||||
);
|
||||
ois.setObjectInputFilter(contextFilter);
|
||||
|
||||
return expectedType.cast(ois.readObject());
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 356: Enhanced Pseudo-Random Number Generators (Java 17)
|
||||
|
||||
**Migration Pattern**: Use new random generator interfaces
|
||||
|
||||
```java
|
||||
import java.util.random.*;
|
||||
|
||||
// Old: Limited Random class
|
||||
Random oldRandom = new Random();
|
||||
int oldValue = oldRandom.nextInt(100);
|
||||
|
||||
// New: Enhanced random generators (Java 17+)
|
||||
RandomGenerator generator = RandomGeneratorFactory
|
||||
.of("Xoshiro256PlusPlus")
|
||||
.create(System.nanoTime());
|
||||
|
||||
RandomGenerator.SplittableGenerator splittableGenerator =
|
||||
RandomGeneratorFactory.of("L64X128MixRandom").create();
|
||||
|
||||
// Better for parallel processing
|
||||
splittableGenerator.splits(4)
|
||||
.parallel()
|
||||
.mapToInt(rng -> rng.nextInt(1000))
|
||||
.forEach(System.out::println);
|
||||
|
||||
// Streamable random values
|
||||
generator.ints(10, 1, 101)
|
||||
.forEach(System.out::println);
|
||||
```
|
||||
|
||||
## I/O and Networking Improvements
|
||||
|
||||
### JEP 380: Unix-Domain Socket Channels (Java 16)
|
||||
|
||||
**Migration Pattern**: Use Unix domain sockets for local IPC
|
||||
|
||||
```java
|
||||
import java.net.UnixDomainSocketAddress;
|
||||
import java.nio.channels.*;
|
||||
|
||||
// Old: TCP sockets for local communication
|
||||
// ServerSocketChannel server = ServerSocketChannel.open();
|
||||
// server.bind(new InetSocketAddress("localhost", 8080));
|
||||
|
||||
// New: Unix domain sockets (Java 16+)
|
||||
public class UnixSocketExample {
|
||||
public void createUnixDomainServer() throws IOException {
|
||||
Path socketPath = Path.of("/tmp/my-app.socket");
|
||||
UnixDomainSocketAddress address = UnixDomainSocketAddress.of(socketPath);
|
||||
|
||||
try (ServerSocketChannel server = ServerSocketChannel.open(StandardProtocolFamily.UNIX)) {
|
||||
server.bind(address);
|
||||
|
||||
while (true) {
|
||||
try (SocketChannel client = server.accept()) {
|
||||
// Handle client connection
|
||||
handleClient(client);
|
||||
}
|
||||
}
|
||||
}
|
||||
}
|
||||
|
||||
public void connectToUnixSocket() throws IOException {
|
||||
Path socketPath = Path.of("/tmp/my-app.socket");
|
||||
UnixDomainSocketAddress address = UnixDomainSocketAddress.of(socketPath);
|
||||
|
||||
try (SocketChannel client = SocketChannel.open(address)) {
|
||||
// Communicate with server
|
||||
ByteBuffer buffer = ByteBuffer.allocate(1024);
|
||||
client.read(buffer);
|
||||
}
|
||||
}
|
||||
|
||||
private void handleClient(SocketChannel client) throws IOException {
|
||||
ByteBuffer buffer = ByteBuffer.allocate(1024);
|
||||
int bytesRead = client.read(buffer);
|
||||
// Process client data
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### JEP 352: Non-Volatile Mapped Byte Buffers (Java 14)
|
||||
|
||||
**Migration Pattern**: Use for persistent memory operations
|
||||
|
||||
```java
|
||||
import java.nio.MappedByteBuffer;
|
||||
import java.nio.channels.FileChannel;
|
||||
import java.nio.file.StandardOpenOption;
|
||||
|
||||
public class PersistentMemoryExample {
|
||||
public void usePersistentMemory() throws IOException {
|
||||
Path nvmFile = Path.of("/mnt/pmem/data.bin");
|
||||
|
||||
try (FileChannel channel = FileChannel.open(nvmFile,
|
||||
StandardOpenOption.READ,
|
||||
StandardOpenOption.WRITE,
|
||||
StandardOpenOption.CREATE)) {
|
||||
|
||||
// Map as persistent memory
|
||||
MappedByteBuffer buffer = channel.map(
|
||||
FileChannel.MapMode.READ_WRITE, 0, 1024,
|
||||
ExtendedMapMode.READ_WRITE_SYNC
|
||||
);
|
||||
|
||||
// Write data that persists across crashes
|
||||
buffer.putLong(0, System.currentTimeMillis());
|
||||
buffer.putInt(8, 12345);
|
||||
|
||||
// Force write to persistent storage
|
||||
buffer.force();
|
||||
}
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
## Build System Configuration
|
||||
|
||||
### Maven Configuration
|
||||
|
||||
```xml
|
||||
<properties>
|
||||
<maven.compiler.source>17</maven.compiler.source>
|
||||
<maven.compiler.target>17</maven.compiler.target>
|
||||
<maven.compiler.release>17</maven.compiler.release>
|
||||
</properties>
|
||||
|
||||
<build>
|
||||
<plugins>
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-compiler-plugin</artifactId>
|
||||
<version>3.11.0</version>
|
||||
<configuration>
|
||||
<release>17</release>
|
||||
<!-- Enable preview features if using JEP 406 -->
|
||||
<compilerArgs>
|
||||
<arg>--enable-preview</arg>
|
||||
</compilerArgs>
|
||||
</configuration>
|
||||
</plugin>
|
||||
|
||||
<!-- For running tests with preview features -->
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-surefire-plugin</artifactId>
|
||||
<version>3.0.0</version>
|
||||
<configuration>
|
||||
<argLine>--enable-preview</argLine>
|
||||
</configuration>
|
||||
</plugin>
|
||||
</plugins>
|
||||
</build>
|
||||
```
|
||||
|
||||
### Gradle Configuration
|
||||
|
||||
```kotlin
|
||||
java {
|
||||
toolchain {
|
||||
languageVersion = JavaLanguageVersion.of(17)
|
||||
}
|
||||
}
|
||||
|
||||
tasks.withType<JavaCompile> {
|
||||
options.release.set(17)
|
||||
// Enable preview features if needed
|
||||
options.compilerArgs.addAll(listOf("--enable-preview"))
|
||||
}
|
||||
|
||||
tasks.withType<Test> {
|
||||
useJUnitPlatform()
|
||||
// Enable preview features for tests
|
||||
jvmArgs("--enable-preview")
|
||||
}
|
||||
```
|
||||
|
||||
## Deprecations and Removals
|
||||
|
||||
### JEP 411: Deprecate the Security Manager for Removal
|
||||
|
||||
**Migration Pattern**: Remove Security Manager dependencies
|
||||
|
||||
```java
|
||||
// Old: Using Security Manager
|
||||
SecurityManager sm = System.getSecurityManager();
|
||||
if (sm != null) {
|
||||
sm.checkPermission(new RuntimePermission("shutdownHooks"));
|
||||
}
|
||||
|
||||
// New: Alternative security approaches
|
||||
// Use application-level security, containers, or process isolation
|
||||
// Most applications don't need Security Manager functionality
|
||||
```
|
||||
|
||||
### JEP 398: Deprecate the Applet API for Removal
|
||||
|
||||
**Migration Pattern**: Migrate from Applets to modern web technologies
|
||||
|
||||
```java
|
||||
// Old: Java Applet (deprecated)
|
||||
public class MyApplet extends Applet {
|
||||
@Override
|
||||
public void start() {
|
||||
// Applet code
|
||||
}
|
||||
}
|
||||
|
||||
// New: Modern alternatives
|
||||
// 1. Convert to standalone Java application
|
||||
public class MyApplication extends JFrame {
|
||||
public MyApplication() {
|
||||
setTitle("My Application");
|
||||
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
|
||||
// Application code
|
||||
}
|
||||
|
||||
public static void main(String[] args) {
|
||||
SwingUtilities.invokeLater(() -> {
|
||||
new MyApplication().setVisible(true);
|
||||
});
|
||||
}
|
||||
}
|
||||
|
||||
// 2. Use Java Web Start alternative (jlink)
|
||||
// 3. Convert to web application using modern frameworks
|
||||
```
|
||||
|
||||
### JEP 372: Remove the Nashorn JavaScript Engine
|
||||
|
||||
**Migration Pattern**: Use alternative JavaScript engines
|
||||
|
||||
```java
|
||||
// Old: Nashorn (removed in Java 17)
|
||||
// ScriptEngine engine = new ScriptEngineManager().getEngineByName("nashorn");
|
||||
|
||||
// New: Alternative approaches
|
||||
// 1. Use GraalVM JavaScript engine
|
||||
ScriptEngine engine = new ScriptEngineManager().getEngineByName("graal.js");
|
||||
|
||||
// 2. Use external JavaScript execution
|
||||
ProcessBuilder pb = new ProcessBuilder("node", "script.js");
|
||||
Process process = pb.start();
|
||||
|
||||
// 3. Use web-based approach or embedded browser
|
||||
```
|
||||
|
||||
## JVM and Performance Improvements
|
||||
|
||||
### JEP 377: ZGC - A Scalable Low-Latency Garbage Collector (Java 15)
|
||||
|
||||
**Migration Pattern**: Enable ZGC for low-latency applications
|
||||
|
||||
```bash
|
||||
# Enable ZGC
|
||||
-XX:+UseZGC
|
||||
-XX:+UnlockExperimentalVMOptions # Not needed in Java 17
|
||||
|
||||
# Monitor ZGC performance
|
||||
-XX:+LogVMOutput
|
||||
-XX:LogFile=gc.log
|
||||
```
|
||||
|
||||
### JEP 379: Shenandoah - A Low-Pause-Time Garbage Collector (Java 15)
|
||||
|
||||
**Migration Pattern**: Enable Shenandoah for consistent latency
|
||||
|
||||
```bash
|
||||
# Enable Shenandoah
|
||||
-XX:+UseShenandoahGC
|
||||
-XX:+UnlockExperimentalVMOptions # Not needed in Java 17
|
||||
|
||||
# Shenandoah tuning
|
||||
-XX:ShenandoahGCHeuristics=adaptive
|
||||
```
|
||||
|
||||
### JEP 341: Default CDS Archives (Java 12) & JEP 350: Dynamic CDS Archives (Java 13)
|
||||
|
||||
**Migration Pattern**: Improved startup performance
|
||||
|
||||
```bash
|
||||
# CDS is enabled by default, but you can create custom archives
|
||||
# Create custom CDS archive
|
||||
java -XX:DumpLoadedClassList=classes.lst -cp myapp.jar com.example.Main
|
||||
java -Xshare:dump -XX:SharedClassListFile=classes.lst -XX:SharedArchiveFile=myapp.jsa -cp myapp.jar
|
||||
|
||||
# Use custom CDS archive
|
||||
java -XX:SharedArchiveFile=myapp.jsa -cp myapp.jar com.example.Main
|
||||
```
|
||||
|
||||
## Testing and Migration Strategy
|
||||
|
||||
### Phase 1: Foundation (Weeks 1-2)
|
||||
|
||||
1. **Update build system**
|
||||
|
||||
- Modify Maven/Gradle configuration for Java 17
|
||||
- Update CI/CD pipelines
|
||||
- Verify dependency compatibility
|
||||
|
||||
2. **Address removals and deprecations**
|
||||
- Remove Nashorn JavaScript engine usage
|
||||
- Replace deprecated Applet APIs
|
||||
- Update Security Manager usage
|
||||
|
||||
### Phase 2: Language Features (Weeks 3-4)
|
||||
|
||||
1. **Implement Records**
|
||||
|
||||
- Convert data classes to records
|
||||
- Add validation in compact constructors
|
||||
- Test serialization compatibility
|
||||
|
||||
2. **Add Pattern Matching**
|
||||
- Convert instanceof chains
|
||||
- Implement type-safe casting patterns
|
||||
|
||||
### Phase 3: Advanced Features (Weeks 5-6)
|
||||
|
||||
1. **Switch Expressions**
|
||||
|
||||
- Convert switch statements to expressions
|
||||
- Use new arrow syntax
|
||||
- Implement complex yield logic
|
||||
|
||||
2. **Text Blocks**
|
||||
- Replace concatenated multi-line strings
|
||||
- Update SQL and HTML generation
|
||||
- Use formatting methods
|
||||
|
||||
### Phase 4: Sealed Classes (Weeks 7-8)
|
||||
|
||||
1. **Design sealed hierarchies**
|
||||
|
||||
- Identify inheritance restrictions
|
||||
- Implement sealed class patterns
|
||||
- Combine with pattern matching
|
||||
|
||||
2. **Testing and validation**
|
||||
- Comprehensive test coverage
|
||||
- Performance benchmarking
|
||||
- Compatibility verification
|
||||
|
||||
## Performance Considerations
|
||||
|
||||
### Records vs Traditional Classes
|
||||
|
||||
- Records are more memory efficient
|
||||
- Faster creation and equality checks
|
||||
- Automatic serialization support
|
||||
- Consider for data transfer objects
|
||||
|
||||
### Pattern Matching Performance
|
||||
|
||||
- Eliminates redundant type checks
|
||||
- Reduces casting overhead
|
||||
- Better JVM optimization opportunities
|
||||
- Use with sealed classes for exhaustiveness
|
||||
|
||||
### Switch Expressions Optimization
|
||||
|
||||
- More efficient bytecode generation
|
||||
- Better constant folding
|
||||
- Improved branch prediction
|
||||
- Use for complex conditional logic
|
||||
|
||||
## Best Practices
|
||||
|
||||
1. **Use Records for Data Classes**
|
||||
|
||||
- Immutable data containers
|
||||
- API data transfer objects
|
||||
- Configuration objects
|
||||
|
||||
2. **Apply Pattern Matching Strategically**
|
||||
|
||||
- Replace instanceof chains
|
||||
- Use with sealed classes
|
||||
- Combine with switch expressions
|
||||
|
||||
3. **Adopt Text Blocks for Multi-line Content**
|
||||
|
||||
- SQL queries
|
||||
- JSON templates
|
||||
- HTML content
|
||||
- Configuration files
|
||||
|
||||
4. **Design with Sealed Classes**
|
||||
|
||||
- Domain modeling
|
||||
- State machines
|
||||
- Algebraic data types
|
||||
- API evolution control
|
||||
|
||||
5. **Leverage Enhanced Random Generators**
|
||||
- Parallel processing scenarios
|
||||
- High-quality random numbers
|
||||
- Statistical applications
|
||||
- Gaming and simulation
|
||||
|
||||
This comprehensive guide enables GitHub Copilot to provide contextually appropriate suggestions when upgrading Java 11 projects to Java 17, focusing on language enhancements, API improvements, and modern Java development practices.
|
||||
464
instructions/java-17-to-java-21-upgrade.instructions.md
Normal file
464
instructions/java-17-to-java-21-upgrade.instructions.md
Normal file
@ -0,0 +1,464 @@
|
||||
---
|
||||
applyTo: ['*']
|
||||
description: "Comprehensive best practices for adopting new Java 21 features since the release of Java 17."
|
||||
---
|
||||
|
||||
# Java 17 to Java 21 Upgrade Guide
|
||||
|
||||
These instructions help GitHub Copilot assist developers in upgrading Java projects from JDK 17 to JDK 21, focusing on new language features, API changes, and best practices.
|
||||
|
||||
## Major Language Features in JDK 18-21
|
||||
|
||||
### Pattern Matching for switch (JEP 441 - Standard in 21)
|
||||
|
||||
**Enhanced switch Expressions and Statements**
|
||||
|
||||
When working with switch constructs:
|
||||
- Suggest converting traditional switch to pattern matching where appropriate
|
||||
- Use pattern matching for type checking and destructuring
|
||||
- Example upgrade patterns:
|
||||
```java
|
||||
// Old approach (Java 17)
|
||||
public String processObject(Object obj) {
|
||||
if (obj instanceof String) {
|
||||
String s = (String) obj;
|
||||
return s.toUpperCase();
|
||||
} else if (obj instanceof Integer) {
|
||||
Integer i = (Integer) obj;
|
||||
return i.toString();
|
||||
}
|
||||
return "unknown";
|
||||
}
|
||||
|
||||
// New approach (Java 21)
|
||||
public String processObject(Object obj) {
|
||||
return switch (obj) {
|
||||
case String s -> s.toUpperCase();
|
||||
case Integer i -> i.toString();
|
||||
case null -> "null";
|
||||
default -> "unknown";
|
||||
};
|
||||
}
|
||||
```
|
||||
|
||||
- Support guarded patterns:
|
||||
```java
|
||||
switch (obj) {
|
||||
case String s when s.length() > 10 -> "Long string: " + s;
|
||||
case String s -> "Short string: " + s;
|
||||
case Integer i when i > 100 -> "Large number: " + i;
|
||||
case Integer i -> "Small number: " + i;
|
||||
default -> "Other";
|
||||
}
|
||||
```
|
||||
|
||||
### Record Patterns (JEP 440 - Standard in 21)
|
||||
|
||||
**Destructuring Records in Pattern Matching**
|
||||
|
||||
When working with records:
|
||||
- Suggest using record patterns for destructuring
|
||||
- Combine with switch expressions for powerful data processing
|
||||
- Example usage:
|
||||
```java
|
||||
public record Point(int x, int y) {}
|
||||
public record ColoredPoint(Point point, Color color) {}
|
||||
|
||||
// Destructuring in switch
|
||||
public String describe(Object obj) {
|
||||
return switch (obj) {
|
||||
case Point(var x, var y) -> "Point at (" + x + ", " + y + ")";
|
||||
case ColoredPoint(Point(var x, var y), var color) ->
|
||||
"Colored point at (" + x + ", " + y + ") in " + color;
|
||||
default -> "Unknown shape";
|
||||
};
|
||||
}
|
||||
```
|
||||
|
||||
- Use in complex pattern matching:
|
||||
```java
|
||||
// Nested record patterns
|
||||
switch (shape) {
|
||||
case Rectangle(ColoredPoint(Point(var x1, var y1), var c1),
|
||||
ColoredPoint(Point(var x2, var y2), var c2))
|
||||
when c1 == c2 -> "Monochrome rectangle";
|
||||
case Rectangle r -> "Multi-colored rectangle";
|
||||
}
|
||||
```
|
||||
|
||||
### Virtual Threads (JEP 444 - Standard in 21)
|
||||
|
||||
**Lightweight Concurrency**
|
||||
|
||||
When working with concurrency:
|
||||
- Suggest Virtual Threads for high-throughput, concurrent applications
|
||||
- Use `Thread.ofVirtual()` for creating virtual threads
|
||||
- Example migration patterns:
|
||||
```java
|
||||
// Old platform thread approach
|
||||
ExecutorService executor = Executors.newFixedThreadPool(100);
|
||||
executor.submit(() -> {
|
||||
// blocking I/O operation
|
||||
httpClient.send(request);
|
||||
});
|
||||
|
||||
// New virtual thread approach
|
||||
try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
|
||||
executor.submit(() -> {
|
||||
// blocking I/O operation - now scales to millions
|
||||
httpClient.send(request);
|
||||
});
|
||||
}
|
||||
```
|
||||
|
||||
- Use structured concurrency patterns:
|
||||
```java
|
||||
// Structured concurrency (Preview)
|
||||
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
|
||||
Future<String> user = scope.fork(() -> fetchUser(userId));
|
||||
Future<String> order = scope.fork(() -> fetchOrder(orderId));
|
||||
|
||||
scope.join(); // Join all subtasks
|
||||
scope.throwIfFailed(); // Propagate errors
|
||||
|
||||
return processResults(user.resultNow(), order.resultNow());
|
||||
}
|
||||
```
|
||||
|
||||
### String Templates (JEP 430 - Preview in 21)
|
||||
|
||||
**Safe String Interpolation**
|
||||
|
||||
When working with string formatting:
|
||||
- Suggest String Templates for safe string interpolation (preview feature)
|
||||
- Enable preview features with `--enable-preview`
|
||||
- Example usage:
|
||||
```java
|
||||
// Traditional concatenation
|
||||
String message = "Hello, " + name + "! You have " + count + " messages.";
|
||||
|
||||
// String Templates (Preview)
|
||||
String message = STR."Hello, \{name}! You have \{count} messages.";
|
||||
|
||||
// Safe HTML generation
|
||||
String html = HTML."<p>User: \{username}</p>";
|
||||
|
||||
// Safe SQL queries
|
||||
PreparedStatement stmt = SQL."SELECT * FROM users WHERE id = \{userId}";
|
||||
```
|
||||
|
||||
### Sequenced Collections (JEP 431 - Standard in 21)
|
||||
|
||||
**Enhanced Collection Interfaces**
|
||||
|
||||
When working with collections:
|
||||
- Use new `SequencedCollection`, `SequencedSet`, `SequencedMap` interfaces
|
||||
- Access first/last elements uniformly across collection types
|
||||
- Example usage:
|
||||
```java
|
||||
// New methods available on Lists, Deques, LinkedHashSet, etc.
|
||||
List<String> list = List.of("first", "middle", "last");
|
||||
String first = list.getFirst(); // "first"
|
||||
String last = list.getLast(); // "last"
|
||||
List<String> reversed = list.reversed(); // ["last", "middle", "first"]
|
||||
|
||||
// Works with any SequencedCollection
|
||||
SequencedSet<String> set = new LinkedHashSet<>();
|
||||
set.addFirst("start");
|
||||
set.addLast("end");
|
||||
String firstElement = set.getFirst();
|
||||
```
|
||||
|
||||
### Unnamed Patterns and Variables (JEP 443 - Preview in 21)
|
||||
|
||||
**Simplified Pattern Matching**
|
||||
|
||||
When working with pattern matching:
|
||||
- Use unnamed patterns `_` for values you don't need
|
||||
- Simplify switch expressions and record patterns
|
||||
- Example usage:
|
||||
```java
|
||||
// Ignore unused variables
|
||||
switch (ball) {
|
||||
case RedBall(_) -> "Red ball"; // Don't care about size
|
||||
case BlueBall(var size) -> "Blue ball size " + size;
|
||||
}
|
||||
|
||||
// Ignore parts of records
|
||||
switch (point) {
|
||||
case Point(var x, _) -> "X coordinate: " + x; // Ignore Y
|
||||
case ColoredPoint(Point(_, var y), _) -> "Y coordinate: " + y;
|
||||
}
|
||||
|
||||
// Exception handling with unnamed variables
|
||||
try {
|
||||
riskyOperation();
|
||||
} catch (IOException | SQLException _) {
|
||||
// Don't need exception details
|
||||
handleError();
|
||||
}
|
||||
```
|
||||
|
||||
### Scoped Values (JEP 446 - Preview in 21)
|
||||
|
||||
**Improved Context Propagation**
|
||||
|
||||
When working with thread-local data:
|
||||
- Consider Scoped Values as a modern alternative to ThreadLocal
|
||||
- Better performance and clearer semantics for virtual threads
|
||||
- Example usage:
|
||||
```java
|
||||
// Define scoped value
|
||||
private static final ScopedValue<String> USER_ID = ScopedValue.newInstance();
|
||||
|
||||
// Set and use scoped value
|
||||
ScopedValue.where(USER_ID, "user123")
|
||||
.run(() -> {
|
||||
processRequest(); // Can access USER_ID.get() anywhere in call chain
|
||||
});
|
||||
|
||||
// In nested method
|
||||
public void processRequest() {
|
||||
String userId = USER_ID.get(); // "user123"
|
||||
// Process with user context
|
||||
}
|
||||
```
|
||||
|
||||
## API Enhancements and New Features
|
||||
|
||||
### UTF-8 by Default (JEP 400 - Standard in 18)
|
||||
|
||||
When working with file I/O:
|
||||
- UTF-8 is now the default charset on all platforms
|
||||
- Remove explicit charset specifications where UTF-8 was intended
|
||||
- Example simplification:
|
||||
```java
|
||||
// Old explicit UTF-8 specification
|
||||
Files.readString(path, StandardCharsets.UTF_8);
|
||||
Files.writeString(path, content, StandardCharsets.UTF_8);
|
||||
|
||||
// New default behavior (Java 18+)
|
||||
Files.readString(path); // Uses UTF-8 by default
|
||||
Files.writeString(path, content); // Uses UTF-8 by default
|
||||
```
|
||||
|
||||
### Simple Web Server (JEP 408 - Standard in 18)
|
||||
|
||||
When needing basic HTTP server:
|
||||
- Use built-in `jwebserver` command or `com.sun.net.httpserver` enhancements
|
||||
- Great for testing and development
|
||||
- Example usage:
|
||||
```java
|
||||
// Command line
|
||||
$ jwebserver -p 8080 -d /path/to/files
|
||||
|
||||
// Programmatic usage
|
||||
HttpServer server = HttpServer.create(new InetSocketAddress(8080), 0);
|
||||
server.createContext("/", new SimpleFileHandler(Path.of("/tmp")));
|
||||
server.start();
|
||||
```
|
||||
|
||||
### Internet-Address Resolution SPI (JEP 418 - Standard in 19)
|
||||
|
||||
When working with custom DNS resolution:
|
||||
- Implement `InetAddressResolverProvider` for custom address resolution
|
||||
- Useful for service discovery and testing scenarios
|
||||
|
||||
### Key Encapsulation Mechanism API (JEP 452 - Standard in 21)
|
||||
|
||||
When working with post-quantum cryptography:
|
||||
- Use KEM API for key encapsulation mechanisms
|
||||
- Example usage:
|
||||
```java
|
||||
KeyPairGenerator kpg = KeyPairGenerator.getInstance("ML-KEM");
|
||||
KeyPair kp = kpg.generateKeyPair();
|
||||
|
||||
KEM kem = KEM.getInstance("ML-KEM");
|
||||
KEM.Encapsulator encapsulator = kem.newEncapsulator(kp.getPublic());
|
||||
KEM.Encapsulated encapsulated = encapsulator.encapsulate();
|
||||
```
|
||||
|
||||
## Deprecations and Warnings
|
||||
|
||||
### Finalization Deprecation (JEP 421 - Deprecated in 18)
|
||||
|
||||
When encountering `finalize()` methods:
|
||||
- Remove finalize methods and use alternatives
|
||||
- Suggest Cleaner API or try-with-resources
|
||||
- Example migration:
|
||||
```java
|
||||
// Deprecated finalize approach
|
||||
@Override
|
||||
protected void finalize() throws Throwable {
|
||||
cleanup();
|
||||
}
|
||||
|
||||
// Modern approach with Cleaner
|
||||
private static final Cleaner CLEANER = Cleaner.create();
|
||||
|
||||
public MyResource() {
|
||||
cleaner.register(this, new CleanupTask(nativeResource));
|
||||
}
|
||||
|
||||
private static class CleanupTask implements Runnable {
|
||||
private final long nativeResource;
|
||||
|
||||
CleanupTask(long nativeResource) {
|
||||
this.nativeResource = nativeResource;
|
||||
}
|
||||
|
||||
public void run() {
|
||||
cleanup(nativeResource);
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
### Dynamic Agent Loading (JEP 451 - Warnings in 21)
|
||||
|
||||
When working with agents or instrumentation:
|
||||
- Add `-XX:+EnableDynamicAgentLoading` to suppress warnings if needed
|
||||
- Consider loading agents at startup instead of dynamically
|
||||
- Update tooling to use startup agent loading
|
||||
|
||||
## Build Configuration Updates
|
||||
|
||||
### Preview Features
|
||||
|
||||
For projects using preview features:
|
||||
- Add `--enable-preview` to compiler and runtime
|
||||
- Maven configuration:
|
||||
```xml
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-compiler-plugin</artifactId>
|
||||
<configuration>
|
||||
<release>21</release>
|
||||
<compilerArgs>
|
||||
<arg>--enable-preview</arg>
|
||||
</compilerArgs>
|
||||
</configuration>
|
||||
</plugin>
|
||||
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-surefire-plugin</artifactId>
|
||||
<configuration>
|
||||
<argLine>--enable-preview</argLine>
|
||||
</configuration>
|
||||
</plugin>
|
||||
```
|
||||
|
||||
- Gradle configuration:
|
||||
```kotlin
|
||||
java {
|
||||
toolchain {
|
||||
languageVersion = JavaLanguageVersion.of(21)
|
||||
}
|
||||
}
|
||||
|
||||
tasks.withType<JavaCompile> {
|
||||
options.compilerArgs.add("--enable-preview")
|
||||
}
|
||||
|
||||
tasks.withType<Test> {
|
||||
jvmArgs("--enable-preview")
|
||||
}
|
||||
```
|
||||
|
||||
### Virtual Threads Configuration
|
||||
|
||||
For applications using Virtual Threads:
|
||||
- No special JVM flags required (standard feature in 21)
|
||||
- Consider these system properties for debugging:
|
||||
```bash
|
||||
-Djdk.virtualThreadScheduler.parallelism=N # Set carrier thread count
|
||||
-Djdk.virtualThreadScheduler.maxPoolSize=N # Set max pool size
|
||||
```
|
||||
|
||||
## Runtime and GC Improvements
|
||||
|
||||
### Generational ZGC (JEP 439 - Available in 21)
|
||||
|
||||
When configuring garbage collection:
|
||||
- Try Generational ZGC for better performance
|
||||
- Enable with: `-XX:+UseZGC -XX:+ZGenerational`
|
||||
- Monitor allocation patterns and GC behavior
|
||||
|
||||
## Migration Strategy
|
||||
|
||||
### Step-by-Step Upgrade Process
|
||||
|
||||
1. **Update Build Tools**: Ensure Maven/Gradle supports JDK 21
|
||||
2. **Language Feature Adoption**:
|
||||
- Start with pattern matching for switch (standard)
|
||||
- Add record patterns where beneficial
|
||||
- Consider Virtual Threads for I/O heavy applications
|
||||
3. **Preview Features**: Enable only if needed for specific use cases
|
||||
4. **Testing**: Comprehensive testing especially for concurrency changes
|
||||
5. **Performance**: Benchmark with new GC options
|
||||
|
||||
### Code Review Checklist
|
||||
|
||||
When reviewing code for Java 21 upgrade:
|
||||
- [ ] Convert appropriate instanceof chains to switch expressions
|
||||
- [ ] Use record patterns for data destructuring
|
||||
- [ ] Replace ThreadLocal with ScopedValues where appropriate
|
||||
- [ ] Consider Virtual Threads for high-concurrency scenarios
|
||||
- [ ] Remove explicit UTF-8 charset specifications
|
||||
- [ ] Replace finalize() methods with Cleaner or try-with-resources
|
||||
- [ ] Use SequencedCollection methods for first/last access patterns
|
||||
- [ ] Add preview flags only for preview features in use
|
||||
|
||||
### Common Migration Patterns
|
||||
|
||||
1. **Switch Enhancement**:
|
||||
```java
|
||||
// From instanceof chains to switch expressions
|
||||
if (obj instanceof String s) return processString(s);
|
||||
else if (obj instanceof Integer i) return processInt(i);
|
||||
// becomes:
|
||||
return switch (obj) {
|
||||
case String s -> processString(s);
|
||||
case Integer i -> processInt(i);
|
||||
default -> processDefault(obj);
|
||||
};
|
||||
```
|
||||
|
||||
2. **Virtual Thread Adoption**:
|
||||
```java
|
||||
// From platform threads to virtual threads
|
||||
Executors.newFixedThreadPool(200)
|
||||
// becomes:
|
||||
Executors.newVirtualThreadPerTaskExecutor()
|
||||
```
|
||||
|
||||
3. **Record Pattern Usage**:
|
||||
```java
|
||||
// From manual destructuring to record patterns
|
||||
if (point instanceof Point p) {
|
||||
int x = p.x();
|
||||
int y = p.y();
|
||||
}
|
||||
// becomes:
|
||||
if (point instanceof Point(var x, var y)) {
|
||||
// use x and y directly
|
||||
}
|
||||
```
|
||||
|
||||
## Performance Considerations
|
||||
|
||||
- Virtual Threads excel with blocking I/O but may not benefit CPU-intensive tasks
|
||||
- Generational ZGC can reduce GC overhead for most applications
|
||||
- Pattern matching in switch is generally more efficient than instanceof chains
|
||||
- SequencedCollection methods provide O(1) access to first/last elements
|
||||
- Scoped Values have lower overhead than ThreadLocal for virtual threads
|
||||
|
||||
## Testing Recommendations
|
||||
|
||||
- Test Virtual Thread applications under high concurrency
|
||||
- Verify pattern matching covers all expected cases
|
||||
- Performance test with Generational ZGC vs other collectors
|
||||
- Validate UTF-8 default behavior across different platforms
|
||||
- Test preview features thoroughly before production use
|
||||
|
||||
Remember to enable preview features only when specifically needed and test thoroughly in staging environments before deploying to production.
|
||||
311
instructions/java-21-to-java-25-upgrade.instructions.md
Normal file
311
instructions/java-21-to-java-25-upgrade.instructions.md
Normal file
@ -0,0 +1,311 @@
|
||||
---
|
||||
applyTo: ['*']
|
||||
description: "Comprehensive best practices for adopting new Java 25 features since the release of Java 21."
|
||||
---
|
||||
|
||||
# Java 21 to Java 25 Upgrade Guide
|
||||
|
||||
These instructions help GitHub Copilot assist developers in upgrading Java projects from JDK 21 to JDK 25, focusing on new language features, API changes, and best practices.
|
||||
|
||||
## Language Features and API Changes in JDK 22-25
|
||||
|
||||
### Pattern Matching Enhancements (JEP 455/488 - Preview in 23)
|
||||
|
||||
**Primitive Types in Patterns, instanceof, and switch**
|
||||
|
||||
When working with pattern matching:
|
||||
- Suggest using primitive type patterns in switch expressions and instanceof checks
|
||||
- Example upgrade from traditional switch:
|
||||
```java
|
||||
// Old approach (Java 21)
|
||||
switch (x.getStatus()) {
|
||||
case 0 -> "okay";
|
||||
case 1 -> "warning";
|
||||
case 2 -> "error";
|
||||
default -> "unknown status: " + x.getStatus();
|
||||
}
|
||||
|
||||
// New approach (Java 25 Preview)
|
||||
switch (x.getStatus()) {
|
||||
case 0 -> "okay";
|
||||
case 1 -> "warning";
|
||||
case 2 -> "error";
|
||||
case int i -> "unknown status: " + i;
|
||||
}
|
||||
```
|
||||
|
||||
- Enable preview features with `--enable-preview` flag
|
||||
- Suggest guard patterns for more complex conditions:
|
||||
```java
|
||||
switch (x.getYearlyFlights()) {
|
||||
case 0 -> ...;
|
||||
case int i when i >= 100 -> issueGoldCard();
|
||||
case int i -> ... // handle 1-99 range
|
||||
}
|
||||
```
|
||||
|
||||
### Class-File API (JEP 466/484 - Second Preview in 23, Standard in 25)
|
||||
|
||||
**Replacing ASM with Standard API**
|
||||
|
||||
When detecting bytecode manipulation or class file processing:
|
||||
- Suggest migrating from ASM library to the standard Class-File API
|
||||
- Use `java.lang.classfile` package instead of `org.objectweb.asm`
|
||||
- Example migration pattern:
|
||||
```java
|
||||
// Old ASM approach
|
||||
ClassReader reader = new ClassReader(classBytes);
|
||||
ClassWriter writer = new ClassWriter(reader, 0);
|
||||
// ... ASM manipulation
|
||||
|
||||
// New Class-File API approach
|
||||
ClassModel classModel = ClassFile.of().parse(classBytes);
|
||||
byte[] newBytes = ClassFile.of().transform(classModel,
|
||||
ClassTransform.transformingMethods(methodTransform));
|
||||
```
|
||||
|
||||
### Markdown Documentation Comments (JEP 467 - Standard in 23)
|
||||
|
||||
**JavaDoc Modernization**
|
||||
|
||||
When working with JavaDoc comments:
|
||||
- Suggest converting HTML-heavy JavaDoc to Markdown syntax
|
||||
- Use `///` for Markdown documentation comments
|
||||
- Example conversion:
|
||||
```java
|
||||
// Old HTML JavaDoc
|
||||
/**
|
||||
* Returns the <b>absolute</b> value of an {@code int} value.
|
||||
* <p>
|
||||
* If the argument is not negative, return the argument.
|
||||
* If the argument is negative, return the negation of the argument.
|
||||
*
|
||||
* @param a the argument whose absolute value is to be determined
|
||||
* @return the absolute value of the argument
|
||||
*/
|
||||
|
||||
// New Markdown JavaDoc
|
||||
/// Returns the **absolute** value of an `int` value.
|
||||
///
|
||||
/// If the argument is not negative, return the argument.
|
||||
/// If the argument is negative, return the negation of the argument.
|
||||
///
|
||||
/// @param a the argument whose absolute value is to be determined
|
||||
/// @return the absolute value of the argument
|
||||
```
|
||||
|
||||
### Derived Record Creation (JEP 468 - Preview in 23)
|
||||
|
||||
**Record Enhancement**
|
||||
|
||||
When working with records:
|
||||
- Suggest using `with` expressions for creating derived records
|
||||
- Enable preview features for derived record creation
|
||||
- Example pattern:
|
||||
```java
|
||||
// Instead of manual record copying
|
||||
public record Person(String name, int age, String email) {
|
||||
public Person withAge(int newAge) {
|
||||
return new Person(name, newAge, email);
|
||||
}
|
||||
}
|
||||
|
||||
// Use derived record creation (Preview)
|
||||
Person updated = person with { age = 30; };
|
||||
```
|
||||
|
||||
### Stream Gatherers (JEP 473/485 - Second Preview in 23, Standard in 25)
|
||||
|
||||
**Enhanced Stream Processing**
|
||||
|
||||
When working with complex stream operations:
|
||||
- Suggest using `Stream.gather()` for custom intermediate operations
|
||||
- Import `java.util.stream.Gatherers` for built-in gatherers
|
||||
- Example usage:
|
||||
```java
|
||||
// Custom windowing operations
|
||||
List<List<String>> windows = stream
|
||||
.gather(Gatherers.windowSliding(3))
|
||||
.toList();
|
||||
|
||||
// Custom filtering with state
|
||||
List<Integer> filtered = numbers.stream()
|
||||
.gather(Gatherers.fold(0, (state, element) -> {
|
||||
// Custom stateful logic
|
||||
return state + element > threshold ? element : null;
|
||||
}))
|
||||
.filter(Objects::nonNull)
|
||||
.toList();
|
||||
```
|
||||
|
||||
## Migration Warnings and Deprecations
|
||||
|
||||
### sun.misc.Unsafe Memory Access Methods (JEP 471 - Deprecated in 23)
|
||||
|
||||
When detecting `sun.misc.Unsafe` usage:
|
||||
- Warn about deprecated memory-access methods
|
||||
- Suggest migration to standard alternatives:
|
||||
```java
|
||||
// Deprecated: sun.misc.Unsafe memory access
|
||||
Unsafe unsafe = Unsafe.getUnsafe();
|
||||
unsafe.getInt(object, offset);
|
||||
|
||||
// Preferred: VarHandle API
|
||||
VarHandle vh = MethodHandles.lookup()
|
||||
.findVarHandle(MyClass.class, "fieldName", int.class);
|
||||
int value = (int) vh.get(object);
|
||||
|
||||
// Or for off-heap: Foreign Function & Memory API
|
||||
MemorySegment segment = MemorySegment.ofArray(new int[10]);
|
||||
int value = segment.get(ValueLayout.JAVA_INT, offset);
|
||||
```
|
||||
|
||||
### JNI Usage Warnings (JEP 472 - Warnings in 24)
|
||||
|
||||
When detecting JNI usage:
|
||||
- Warn about upcoming restrictions on JNI usage
|
||||
- Suggest adding `--enable-native-access` flag for applications using JNI
|
||||
- Recommend migration to Foreign Function & Memory API where possible
|
||||
- Add module-info.java entries for native access:
|
||||
```java
|
||||
module com.example.app {
|
||||
requires jdk.unsupported; // for remaining JNI usage
|
||||
}
|
||||
```
|
||||
|
||||
## Garbage Collection Updates
|
||||
|
||||
### ZGC Generational Mode (JEP 474 - Default in 23)
|
||||
|
||||
When configuring garbage collection:
|
||||
- Default ZGC now uses generational mode
|
||||
- Update JVM flags if explicitly using non-generational ZGC:
|
||||
```bash
|
||||
# Explicit non-generational mode (will show deprecation warning)
|
||||
-XX:+UseZGC -XX:-ZGenerational
|
||||
|
||||
# Default generational mode
|
||||
-XX:+UseZGC
|
||||
```
|
||||
|
||||
### G1 Improvements (JEP 475 - Implemented in 24)
|
||||
|
||||
When using G1GC:
|
||||
- No code changes required - internal JVM optimization
|
||||
- May see improved compilation performance with C2 compiler
|
||||
|
||||
## Vector API (JEP 469 - Eighth Incubator in 25)
|
||||
|
||||
When working with numerical computations:
|
||||
- Suggest Vector API for SIMD operations (still incubating)
|
||||
- Add `--add-modules jdk.incubator.vector`
|
||||
- Example usage:
|
||||
```java
|
||||
import jdk.incubator.vector.*;
|
||||
|
||||
// Traditional scalar computation
|
||||
for (int i = 0; i < a.length; i++) {
|
||||
c[i] = a[i] + b[i];
|
||||
}
|
||||
|
||||
// Vectorized computation
|
||||
var species = IntVector.SPECIES_PREFERRED;
|
||||
for (int i = 0; i < a.length; i += species.length()) {
|
||||
var va = IntVector.fromArray(species, a, i);
|
||||
var vb = IntVector.fromArray(species, b, i);
|
||||
var vc = va.add(vb);
|
||||
vc.intoArray(c, i);
|
||||
}
|
||||
```
|
||||
|
||||
## Compilation and Build Configuration
|
||||
|
||||
### Preview Features
|
||||
|
||||
For projects using preview features:
|
||||
- Add `--enable-preview` to compiler arguments
|
||||
- Add `--enable-preview` to runtime arguments
|
||||
- Maven configuration:
|
||||
```xml
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-compiler-plugin</artifactId>
|
||||
<configuration>
|
||||
<release>25</release>
|
||||
<compilerArgs>
|
||||
<arg>--enable-preview</arg>
|
||||
</compilerArgs>
|
||||
</configuration>
|
||||
</plugin>
|
||||
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-surefire-plugin</artifactId>
|
||||
<configuration>
|
||||
<argLine>--enable-preview</argLine>
|
||||
</configuration>
|
||||
</plugin>
|
||||
```
|
||||
|
||||
- Gradle configuration:
|
||||
```kotlin
|
||||
java {
|
||||
toolchain {
|
||||
languageVersion = JavaLanguageVersion.of(25)
|
||||
}
|
||||
}
|
||||
|
||||
tasks.withType<JavaCompile> {
|
||||
options.compilerArgs.add("--enable-preview")
|
||||
}
|
||||
|
||||
tasks.withType<Test> {
|
||||
jvmArgs("--enable-preview")
|
||||
}
|
||||
```
|
||||
|
||||
## Migration Strategy
|
||||
|
||||
### Step-by-Step Upgrade Process
|
||||
|
||||
1. **Update Build Tools**: Ensure Maven/Gradle supports JDK 25
|
||||
2. **Update Dependencies**: Check for JDK 25 compatibility
|
||||
3. **Handle Warnings**: Address deprecation warnings from JEPs 471/472
|
||||
4. **Enable Preview Features**: If using pattern matching or other preview features
|
||||
5. **Test Thoroughly**: Especially for applications using JNI or sun.misc.Unsafe
|
||||
6. **Performance Testing**: Verify GC behavior with new ZGC defaults
|
||||
|
||||
### Code Review Checklist
|
||||
|
||||
When reviewing code for Java 25 upgrade:
|
||||
- [ ] Replace ASM usage with Class-File API
|
||||
- [ ] Convert complex HTML JavaDoc to Markdown
|
||||
- [ ] Use primitive patterns in switch expressions where applicable
|
||||
- [ ] Replace sun.misc.Unsafe with VarHandle or FFM API
|
||||
- [ ] Add native-access permissions for JNI usage
|
||||
- [ ] Use Stream gatherers for complex stream operations
|
||||
- [ ] Update build configuration for preview features
|
||||
|
||||
### Testing Considerations
|
||||
|
||||
- Test with `--enable-preview` flag for preview features
|
||||
- Verify JNI applications work with native access warnings
|
||||
- Performance test with new ZGC generational mode
|
||||
- Validate JavaDoc generation with Markdown comments
|
||||
|
||||
## Common Pitfalls
|
||||
|
||||
1. **Preview Feature Dependencies**: Don't use preview features in library code without clear documentation
|
||||
2. **Native Access**: Applications using JNI directly or indirectly may need `--enable-native-access` configuration
|
||||
3. **Unsafe Migration**: Don't delay migrating from sun.misc.Unsafe - deprecation warnings indicate future removal
|
||||
4. **Pattern Matching Scope**: Primitive patterns work with all primitive types, not just int
|
||||
5. **Record Enhancement**: Derived record creation requires preview flag in Java 23
|
||||
|
||||
## Performance Considerations
|
||||
|
||||
- ZGC generational mode may improve performance for most workloads
|
||||
- Class-File API reduces ASM-related overhead
|
||||
- Stream gatherers provide better performance for complex stream operations
|
||||
- G1GC improvements reduce JIT compilation overhead
|
||||
|
||||
Remember to test thoroughly in staging environments before deploying Java 25 upgrades to production systems.
|
||||
Loading…
x
Reference in New Issue
Block a user